Some antigens are highly immunogenic and are capable alone of eliciting protective immune responses. Other antigens, however, fail to induce a protective immune response or induce only a weak immune response. A frequent difficulty with active immunization protocols is that the vaccine antigen does not possess sufficient immunogenicity to promote a strong immune response, and therefore a sufficient level of protection against subsequent challenge by the same antigen. In addition, certain antigens may elicit only weak cell-mediated or antibody response. For many antigens, both a strong humoral response and a strong cell-mediated response is desirable.
For decades, researchers have experimented with diverse compounds to increase the immunogenicity of vaccines, as well as other pharmaceutical compositions. Immunopotentiators, also known as adjuvants, of vaccines are compositions of matter that facilitate a strong immune response to a vaccine. In addition, the relatively weak immunogenicity of certain novel recombinant antigens has required adjuvants to be more potent. Vaccine adjuvants have different modes of action, affecting the immune response both quantitatively and qualitatively. Such modes of action can be by mobilizing T cells, acting as depots and altering lymphocyte circulation so that these cells remain localized in draining lymph nodes. They may also serve to focus antigen at the site of immunization, thereby allowing antigen specific T cells and B cells to interact more efficiently with antigen-presenting cells. Adjuvants may also stimulate proliferation and differentiation of T cells and have effects on B cells, such as enhancing the production of different Ig isotypes. Further, adjuvants may stimulate and affect the behavior of antigen-presenting cells, particularly macrophages, rendering them more effective for presenting antigen to T cells and B cells.
In the development of some vaccines and immunogenic compositions, there is a trend to use smaller and well defined immunogenic and protective materials. Recent advances in molecular genetics, protein biochemistry, peptide chemistry, and immunobiology have provided economical and efficient technologies to identify and produce large quantities of pure antigens from various pathogens. However, some such materials may not be sufficiently immunogenic, due to either their small size (especially synthetic peptides) or the lack of intrinsic immunostimulatory properties thereof.
Immunogenicity can be significantly improved if these antigens are co-administered with adjuvants. Adjuvants can also attract cells of the immune system to an antigen depot and stimulate such cells to elicit immune responses.
Immunostimulatory agents or adjuvants have been used for many years to improve the host immune responses to, for example, vaccines. Intrinsic adjuvants, such as lipopolysaccharides, normally are the components of the killed or attenuated bacteria used as vaccines. Extrinsic adjuvants are immunomodulators which are typically non-covalently linked to antigens and are formulated to enhance the host immune responses. Thus, adjuvants have been identified that enhance the immune response to antigens delivered parenterally. Some of these adjuvants are toxic, however, and can cause undesirable side-effects, making them unsuitable for use in humans and many animals. Indeed, only aluminum hydroxide and aluminum phosphate (collectively commonly referred to as alum) are routinely used as adjuvants in human and veterinary vaccines. The efficacy of alum in increasing antibody responses to diptheria and tetanus toxoids is well established and, more recently, a HBsAg vaccine has been adjuvanted with alum. While the usefulness of alum is well established for some applications, it has limitations. For example, alum is ineffective for influenza vaccination and inconsistently elicits a cell mediated immune response. The antibodies elicited by alum-adjuvanted antigens are mainly of the IgG1 isotype in the mouse, which may not be optimal for protection by some vaccinal agents.
A wide range of extrinsic adjuvants can provoke potent immune responses to antigens. These include saponins complexed to membrane protein antigens (immune stimulating complexes), pluronic polymers with mineral oil, killed mycobacteria in mineral oil, Freund's complete adjuvant, bacterial products, such as muramyl dipeptide (MDP) and lipopolysaccharide (LPS), as well as lipid A, and liposomes.
To efficiently induce humoral immune responses (HIR) and cell-mediated immunity (CMI), immunogens are emulsified in adjuvants. Many adjuvants are toxic, inducing granulomas, acute and chronic inflammations (Freund's complete adjuvant, FCA), cytolysis (saponins and Pluronic polymers) and pyrogenicity, arthritis and anterior uveitis (LPS and MDP). Although FCA is an excellent adjuvant and widely used in research, it is not licensed for use in human or veterinary vaccines because of its toxicity. Freund's Complete adjuvant (FCA) is an emulsion containing mineral oil and killed mycobacteria in saline. Freund's incomplete adjuvant (FIA) omits the mycobacteria. Both FIA and FCA induce good humoral (antibody) immunity, and FCA additionally induces high levels of cell-mediated immunity. However, neither FCA nor FIA are acceptable for clinical use due to the side effects. In particular, mineral oil is known to cause granulomas and abscesses, and Mycobacterium tuberculosis is the agent responsible for tuberculosis.
There have been many substances that have been tried to be used as adjuvants, such as the lipid-A portion of gram negative bacterial endotoxin, and trehalose dimycolate of mycobacteria. The phospholipid lysolecithin exhibited adjuvant activity (Arnold et al., Eur. J. Immunol. 9:363–366, 1979). Some synthetic surfactants exhibited adjuvant activity, including dimethyldioctadecyl ammonium bromide (DDA) and certain linear polyoxypropylenepolyoxyethylene (POP-POE) block polymers (Snippe et al., Int. Arch. Allergy Appl. Immunol. 65:390–398, 1981; and Hunter et al., J. Immunol. 127:1244–1250, 1981) While these natural or synthetic surfactants demonstrate some degree of adjuvant activity, they do not demonstrate the degree of immunopotentiation (i.e., adjuvant activity) as FCA or FIA.
Another approach has looked to break down the adjuvant effect from mycobacteria and determine adjuvant activity from a muramyl-peptide in the cell wall. The smallest fragment of this molecule that retains adjuvant activity is N-acetyl-muramyl-L-alanyl-D-isoglutamine, which is also called muramyl dipeptide (MDP) (Ellouz et al., Biochem. & Biophys. Res. Comm. 1317–1325, 1974). There have been many MDP derivatives prepared as vaccine adjuvants and described in U.S. Pat. Nos. 4,158,052; 4,323,559; 4,220,637; 4,323,560; 4,409,209; 4,423,038; 4,185,089; 4,406,889; 4,082,735; 4,082,736; 4,427,659; 4,461,761; 4,314,998; 4,101,536; and 4,369,178. Each of these disclosed MDP derivatives were weakly effective at stimulating the immune system when administered in aqueous solution, but the activity generally falls short of FCA or FIA.
Vaccine adjuvants are useful for improving an immune response obtained with any particular antigen in a vaccine composition. Adjuvants are used to increase the amount of antibody and effector T cells produced and to reduce the quantity of antigen and the frequency of injection. Although some antigens are administered in vaccines without an adjuvant, there are many antigens that lack sufficient immunogenicity to stimulate a useful immune response in the absence of an effective adjuvant. Adjuvants also improve the immune response from “self-sufficient” antigens, in that the immune response obtained may be increased or the amount of antigen administered may be reduced.
Many tumors express proteins that can serve as tumor-specific antigens. Such antigens can be processed via the MHC class I pathway and presented to CD8+ T cells as has been shown for the MAGE-1 gene expressed in melanoma (1), p53 in breast cancer (2), heat shock proteins (3,4), and glycosylation variants of proteins such as MUC-1 mucin (5).
However, tumors generally lack co-stimulatory molecules and hence cannot provide the requisite two signals to activate humor-specific CTL (6). Consequently, spontaneous tumors generally fail to stimulate immunity.
Tumors have been genetically engineered to express co-stimulators [reviewed in (7) {8276/id Viret & Lindemann 1997} (8)] and the modified cells can induce rejection if given before the tumor is transplanted in model systems (9). In a clinical setting, however, tumors presenting antigen in the absence of co-stimulators will likely induce tolerance of the relevant T cells before the tumor is detected (10). Such tumor-specific tolerance may prevent induction of immunity by genetically engineered, autologous tumor cells. Tolerance induction by tumors is not well characterized but recent reports (11,12) demonstrate that tumors induced tolerance in certain animal models.
The present inventors have recently found that the antitussive noscapine and its derivatives are useful in the treatment of neoplastic diseases. Noscapine is used as an antitussive drug and has low toxicity in humans. Noscapine arrests mammalian cells at mitosis, causes apoptosis in cycling cells, and has potent antitumor activity. Noscapine is an alkaloid from opium, and is readily available as a commercial byproduct in the commercial production of prescription opiates. It has been discovered that noscapine promotes assembly of tubulin subunits.
The present inventors have now discovered that noscapine and its derivatives are useful as adjuvant compositions to augment cell mediated immunity. In particular, noscapine and its derivatives can be used to enhance cytolytic responses to a tumor cell or as a vaccine adjuvant.